This invention relates to antennas and in particular to antennas for producing more than one polarisation of RF radio waves.
Various forms of RF antenna are known for producing vertical, horizontal, right-hand circular or left-hand circular polarisation of RF radio waves. FIG. 1 shows two arrangements for producing horizontally polarised RF waves. FIG. 1a shows a slotted cylinder arrangement in which RF signals are received on a coaxial line coupled to a slot within a cylinder. FIG. 1b shows a printed circuit antenna known as an Alford loop having two parallel conductors each arranged in a plane and separated by a dielectric.
FIG. 2 shows various arrangements of antenna for vertical polarisation. FIG. 2a is a discone arrangement, FIG. 2b is a monopole arrangement and FIG. 2c is a sleeved dipole arrangement.
A circularly polarised antenna may be formed from horizontally oriented crossed diploes with a 90° phase shift between them to produce circular polarisation.